With the development of data storage techniques, various data storage devices now provide users with higher data storage capacity, and also their speed of accessing data has been increased greatly. So far various RAID-based data storage systems have been developed to increase data reliability. When one or more disks in a storage system fail, a new backup disk needs to be introduced to the storage system, data in failed disks can be recovered from data in other disks operating normally.
The storage system may allocate storage spaces in corresponding sizes according to requests of different users. For example, the storage system may indicate the allocated storage space in the form of Logic Unit Number (LUN). However, since the allocated storage space is defined in light of the requested size, once a corresponding storage space is allocated for a user, the size of the space is fixed and cannot be adjusted during use as the user demands.